1. Field of the Invention
This invention relates to a method of making a composite sandwich panel comprising a carbon nanotube structure.
2. Description of Related Art
Japanese patent application number JP 2010037660 A to Furuzuki discloses that a carbon nanotube (CNT) containing paper can be produced by adding carbon nanotubes in a mono-dispersed state in an amount of 1 to 50 wt. % relative to the total amount of solid materials during a papermaking process. The constituent fiber component of the CNT-containing paper is a natural fiber, a synthetic fiber, an inorganic fiber, a metallic fiber or the like.
Chinese patent application number CN 101284661 A to Wang teaches the preparation of carbon nanotube sheets by adding carbon nanotube material to a solution comprising metallic particles, performing flocculation treatment, adding a reducing agent and separating a nanotube flocculent structure from the solution.
PCT publication WO 2011054008 A to Shah describes a composition including a carbon nanotube (CNT) infused aramid fiber material that includes an aramid fiber material of spoolable dimensions, a barrier coating conformally disposed about the aramid fiber material, and carbon nanotubes (CNT's) infused to the aramid fiber material. The infused CNTs are uniform in length and uniform in density.
Core structures for composite sandwich panels from high modulus high strength fiber nonwoven sheets, mostly in the form of honeycomb, are used in different applications but primarily in the aerospace industry where strength to weight or stiffness to weight ratios have very high values. For example, U.S. Pat. No. 5,137,768 to Lin describes a honeycomb core made from a high-density wet-laid nonwoven comprising 50 wt. % or more of p-aramid fiber with the rest of the composition being a binder and other additives.
Publication WO2011/062980 describes a honeycomb core made from paper comprising 20-85 weight percent of carbon fiber floc. The carbon fibers have a non-round cross sectional aspect ratio of at least 1.5:1. The paper has a fiber volume fraction of at least 35%. The arithmetic mean length of the carbon fibers is at least 0.5 mm. and a length weighted mean length of at least 0.9 mm. Publication WO2011/062980 describes a folded core made from the same paper
There is an ongoing need to provide composite sandwich panels having improved mechanical properties such as stiffness, strength, toughness, and impact resistance. This is particularly true for structures used in aircraft, trains, and boats. Such improvements may be achieved by efficient incorporation of a carbon nanotube structure into the sandwich panel.